Bubbles formed in water are classified into milli bubbles or micro bubbles (or even, micro-nano bubbles, nano bubbles and the like) depending on their size. The milli bubbles are relatively large bubbles. The milli bubbles rise up in the water rapidly, break on the water surface and finally disappear. In contrast, bubbles having diameters equal to or less than 50 μm have following special properties. The above bubbles are very small and therefore stay longer in the water. Also, the bubbles have excellent gas solubility in the water. As a result, the bubbles further reduce in size in the water and finally disappear (i.e., dissolve completely) in the water. Such bubbles have generally come to be known as micro bubbles (refer to Non-Patent Document 1). In the present specification, the term “fine bubbles” generally indicates the above micro bubbles and also indicates bubbles having smaller diameters such as micro-nano bubbles (bubbles having diameters equal to or greater than 10 nm and less than 1 μm) and nano bubbles (having diameters less than 10 nm).
Recently, such fine bubbles are used in many applications, and there have been suggested various showers specifically used in bath rooms or the like with built-in bubble generating mechanisms (refer to Patent Documents 1 to 5). The bubble generating mechanisms assembled in the showers disclosed in Patent Documents are classified into two types of a mechanism of Patent Document 1 and another mechanism of Patent Documents 2 to 5. In the mechanism of Patent Document 1 (also referred to as a two-phase-flow swirl-type mechanism), swirling flow generating blades are assembled into a head part that sprays a shower water flow. A vortex flow formed by the blades is mixed with external air suctioned by vacuum through a narrow hole formed in a blade shaft portion, thereby mixing the gas and the liquid. In the other mechanism (a cavitation type mechanism) of Patent Documents 2 to 5, a restriction mechanism such as a Venturi tube is assembled into a shower main body (a handle part extending from a head part). When water passes through the restriction mechanism at an increased flow rate, a pressure reduction effect generated based on Bernoulli's principle causes the air dissolved in the water to deposit as fine bubbles.